In recent years, vicinal diamines have been found to be useful in an uncommonly wide variety of applications. In particular, vicinal diamines play an important role in direct metal chelation. Also, vicinal diamines have been found to be a key architectural component for a wide range of natural products and also for medicinally active compounds. Therefore, studies directed toward the synthesis and preparation of vicinal diamine systems have intensified.
Rapid advances have occurred in the development of synthetic methods for preparing vicinal diamines, however, most of these new synthetic methods have the disadvantage of limited scope or limited stereoselectivity. Several recently developed synthetic methods are based upon the generation of vicinal diazides, dinitro, and other related nitrogen oxidation state equivalents, and their subsequent reduction to a corresponding diamine. These methods have several disadvantages, including the lack of stereoselectivity, susceptibility to side-reactions upon reduction, and the necessity of handling dangerous, explosive intermediates, such as azides.
Other new synthetic methods are based upon the ring opening of aziridines with ammonia or amines, or those which employ intramolecular cyclizations. These methods offer a greater degree of stereocontrol than those mentioned above, but have the disadvantage of requiring long chemical synthesis sequences in order to set up the key nitrogen installation step.
Several other synthetic methods have been developed, however, all have exhibited disadvantages. In particular, active metal mediated reductive dimerization of Schiff bases has been thoroughly examined, and has been found useful only for the preparation of aromatic secondary vicinal diamines. Further, niobium promoted coupling of nitriles or N-(trimethylsilyl)imines has been found applicable to the synthesis of primary diamines, but has the disadvantages of unpredictable stereoselectivity and requiring the use of specialized reagents. Moreover, the reductive amination of .alpha.-amino aldehydes and .alpha.-amino ketones, the reduction of .alpha.-amino amides and .alpha.-amino nitriles and the reduction of or addition to .alpha.-amino imines have all proved to be useful reaction synthesis techniques, but are greatly limited in utility because of the accessibility of suitable starting materials. Also, these techniques generally require the preliminary modification of amino acids as chiral educts in order to extend to enantioselective synthesis.